Known gas laser generators include a longitudinal enclosure containing an active gas and means for creating a travelling wave running from one end of the enclosure to the other at a velocity equal to that of the propagation speed of a light emission stimulated in the active gas.
Laser generators of this type are generally provided with a flat electric line constituted by two metal plates having different electric potentials and an insulating plate inserted between the metal plates and a trigger circuit capable of inducing a practically point electrical discharge between the metal plates so as to create a travelling current wave in this line. The active gas medium is contained in a longitudinal slot in one of the metal plates of the line on the path of the travelling current wave.
When observing the outgoing laser beam emitted by a generator of this type, one notes that it looks as though the beam were formed of two elementary beams diverging respectively from two points placed symmetrically to an emission axis; the distance between these two points is directly related to the width of the slot containing the active gas medium.
In order to correct the divergence of the outgoing beam, generally an optical convergent lens centered on the emission axis is placed on the path taken by the elementary beams in a manner ensuring that one of its focal planes contains the two points from where the elementary beams appear to originate. The divergence proper to each of the elementary beams is then corrected, but after having passed through the lens the outgoing beam still shows a residual divergence caused by the double origin of this beam. This residual divergence which is equal to the quotient of the distance between the two points and the focal distance of the lens, is in general, considerable and in practice, very disturbing.
Preferred embodiments of the present invention reduce this disadvantage and provide a gas laser device whose outgoing beam, emitted under the influence of a travelling wave, has a divergence considerably smaller than that of beams generated by known laser generator devices as described above.